The invention is in the field of electrically conductive connections and is to be applied in the structural design of a welded connection between an end electrode of a gas-filled discharge pathxe2x80x94like a surge arrester or a switching dischargerxe2x80x94and a lead.
It is known in gas-filled surge arresters or gas-filled switching dischargers with end electrodes, which are fashioned cup-shaped, to provide the end electrodes (composed of copper) with a raised, peg-like terminal region that is arranged centrally relative to the solder flange of the end electrode in the cup-like depression of the electrode and the peg-like terminal region is integrally provided or formed with the electrode by extrusion during manufacture (U.S. Pat. No. 4,266,260 A). In order to assure a dependable positive connection between this terminal region and the one end of the lead by resistance welding, it is also known to dimension the raised terminal region in a specific way dependent on the diameter of the lead (EP 0 034 360 B1/U.S. Pat. No. 4,362,962 A). Relatively high currents, that cause considerable heating of the end electrode and thus also thermally load the adjacent solder point to the insulator, flow during manufacture of such welded connections. This connection technique, moreover, can hardly be applied given leads having a diameter  less than 1 mm.
Proceeding from an electrically conductive connection between a lead and a raised terminal region of the electrode, the invention is therefore based on the object of designing the positive connection so that it can be more simply produced in fabrication-oriented terms and can also be utilized for wire diameters below 1 mm.
For achieving this object, it is inventively provided that the raised terminal region is provided with an axial blind hole, and that the lead has its one end introduced into the blind hole and is joined to the raised terminal region by laser welding. Expediently, a plurality of weld points are provided uniformly distributed over the circumference of the raised terminal region.
As a result of the known employment of a laser beam for supplying the welding energy, a positive connection fashioned in this way can be produced with very high reproducibility of the welding parameters and, accordingly, with dependable connection quality. The coaxialism between lead and solder flange of the electrode is thereby determined solely by the coaxialism of the blind hole relative to the solder hole. The production of the connection is accompanied by only a slight thermal load on the arrester. The new connection can thereby be utilized both for galvanically coated or non-coated electrodes of copper or of ferrous and non-ferrous alloys, particularly iron-nickel alloys, as well as for bare or nickel-coated or tinned copper wires, whereby a nickel or tin plating improves the degree of absorption for the laser light. Layer thicknesses from 1 through 100 xcexcm come into consideration for the coating. A layer thickness of 6 xcexcm has proven advantageous. It is thereby advantageous for the welding process that the laser beam can be very precisely positioned and dosed in view of its thermal energy. Thus, material from the dome of the raised terminal region is melted first during the welding and then unites with the subsequently melted material of the wire end.
The terminal region of the end electrode provided according to the invention can be cylindrically fashioned. However, a design as a conoidal frustum is advantageous because the laser beam can then be positioned so that it preferably impinges the generated surface of the conoidal frustum at a right angle so that an optimum heat absorption is established.
The dimensions of the conoidal frustum-shaped terminal region should lie within the following limits given wire diameters from 0.5 through 3 mm:
Taking simple manufacturability of the end electrodes by cold extrusion into consideration, the blind hole should thereby be fashioned slightly conical.
Exemplary embodiments of the new welded connection are shown in the Figures and a modification of the design of that of a lead that is to be welded is also shown.